The present invention relates to a tool coupling for connecting a tool head and a tool holder to provide security against rotation and axial distortion, with the tool head serving as a cutting tool and comprising a partially conical shank or shaft and an annular abutment collar and with the tool holder having a receptacle corresponding to the shank and having a corresponding abutment collar. Such couplings are required, in particular, for machine tools which are automatically attached and manipulated.
When tools are changed in automatic cutting machinery, tools having steep angle tapered shafts are received in a conical sleeve where they are axially tensioned. Steep angle tapered shafts for tools and cutting equipment are defined, for example, in German Standard DIN No. 2080. The steep angle taper has the advantage that its conical shape permits easy introduction into the corresponding receptacle and easy, correct positioning. On the other hand, however, there are drawbacks. The tools to be exchanged are rather large and heavy. Moreover, considerable cutting forces sometimes act on the tapered shaft at a right angle to the longitudinal axis of the tool, and these forces are insufficiently absorbed by the tool faces. An attempt has been made to overcome the lack of planar contact of such a coupling by providing better support for the tool head using a retaining means flange that is brought into contact with the frontal face of the tool holder. However, such a coupling requires precision manufacture because the connection is critical. If there is even a slight deviation, some play exists between the tapered shaft and the correspondingly shaped receiving sleeve if the flange is in contact, or the flange does not find its abutment if the tapered shaft and sleeve are seated on one another in a good fit.
German Pat. No. 3,225,173 already discloses a connecting device in which adapters are provided between the frontal face of a spindle and a rotating collar of the steep angle tapered shaft. These adapters are connected with a retaining means flange by means of holding screws and are supported at the frontal face. This produces planar contact as well as full support of the tapered shaft. However, because of the problem of manufacturing tolerances, this system cannot be employed for the automatic exchange of tools. In particular, such a coupling is impossible to use in practice if a variety of tools and tool holders are combined.
German Published Patent Application [without examination] No. 3,314,591 discloses a clamping system with planar contact. The system includes a short conical fitting section in which the conical sleeve of a tool holder and the pilot tapered shaft of a tool head are configured in such a way that the tapered shaft comes to bear only at the smallest portion of its diameter, while at the larger portion there is air in the area of the planar contact. Planar contact is allegedly assured in that either the conical taper or the conical sleeve deforms enough elastically in the region of their smallest diameters that planar contact is achieved. These clamping systems, however, do not prevent the tool from escaping to the side due to play at the larger diameter of the conical surfaces if there is a unilateral load, and thus the tool is limited in function and performance capability.